readthedocs.org: New Docker client returning timeout on EXEC

https://sentry.io/read-the-docs/readthedocs-org/issues/533022676/

timeout: timed out
(10 additional frame(s) were not displayed)
...
  File "readthedocs/doc_builder/environments.py", line 472, in run
    return super(BuildEnvironment, self).run(*cmd, **kwargs)
  File "readthedocs/doc_builder/environments.py", line 307, in run
    return self.run_command_class(cls=self.command_class, cmd=cmd, **kwargs)
  File "readthedocs/doc_builder/environments.py", line 478, in run_command_class
    return super(BuildEnvironment, self).run_command_class(*cmd, **kwargs)
  File "readthedocs/doc_builder/environments.py", line 346, in run_command_class
    build_cmd.run()
  File "readthedocs/doc_builder/environments.py", line 234, in run
    output = client.exec_start(exec_id=exec_cmd['Id'], stream=False)

(Build) [astropy:latest] timed out